1. Field of the Invention
The present invention relates to a method of producing a ceramic electronic part using a ceramic sintered body with an internal electrode, such as a layered capacitor, and more particularly to a method of producing a ceramic electronic part in which the polishing step carried out to expose the internal electrode from an outside surface of the ceramic sintered body is improved.
2. Description of the Related Art
When producing a ceramic electronic part including an internal electrode, such as a layered capacitor, it is necessary that the internal electrode be reliably electrically connected to an external electrode at the final stage. Ordinarily, the ceramic sintered body is formed by placing unsintered ceramic layers one on top of the other with an internal electrode located between each adjacent pair of electrodes, and then firing the unsintered ceramic layered body. However, in the ceramic sintered body formed in the above-described way, the contraction rates of the internal electrodes and the ceramic layers during the firing process are different, so that the internal electrodes may not be exposed from the outside surface of the ceramic sintered body. This is illustrated in FIGS. 10 and 11.
FIG. 10 is a vertical sectional view of a ceramic sintered body used in a layered capacitor. A plurality of internal electrodes 52a to 52f are formed in the ceramic sintered body 51. Because external electrodes are formed at end surfaces 51a and 51b of the ceramic sintered body 51 during a later step, it is necessary that the internal electrodes 52a, 52c, and 52e be reliably exposed from the end surface 51a, and that the internal electrodes 52b, 52d, and 52f be reliably exposed at the end surface 51b. 
However, since the contraction rates of the ceramic layers and the internal electrodes are different the internal electrodes are often located inward of the end surfaces after sintering and are thus often not exposed from the end surface 51a or 51b. This is shown, by way of example, in FIG. 11 wherein the internal electrode 52a is disposed inward from the end surface 51a. 
Conventionally, in order to expose the internal electrodes 52a to 52f, a wet-polishing method is used to polish the aforementioned ceramic sintered body 51 that has been obtained. More specifically, a plurality of the sintered bodies 51, an abrasive, and water are placed into a barrel and the barrel is rotated in order to polish the ceramic sintered bodies 51, thereby exposing the internal electrodes 52a to 52f from the end surface 51a or 51b. 
Water is used as a shock-absorbing material to reduce impact force. The use of water prevents cracking of the ceramic sintered bodies 51 caused by collisions of the ceramic sintered bodies 51 themselves and collisions of the abrasive and the ceramic sintered bodies 51.
In addition to the above-described wet-barrel polishing method, a sandblast method is sometimes used to polish the end surfaces 51a and 51b of the ceramic sintered bodies 51. In the sandblast method, the ceramic sintered bodies 51 are held by a holder having a plurality of holes arranged in a row, and the exposed end surfaces 51a and 51b are subjected to sandblasting.
The above-described wet-barrel polishing method allows the internal electrodes 52a to 52f to be reliably exposed from the end surface 51a or 51b of the ceramic sintered bodies 51, but has the problem of water flowing into the ceramic sintered bodies 51. More specifically, the water used as the shock-absorbing material tends to move in through the interfaces between the internal electrodes 52a to 52f and the ceramics layers. This water cannot be easily removed from the ceramic sintered bodies 51, and reacts during firing of the external electrodes carried out later, thereby accelerating peeling at the interfaces between the ceramics and the internal electrodes 52a to 52f. 
When the conventional wet-barrel polishing method using water is used, interlayer peeling, called delamination, tends to occur in the layered capacitors obtained at the final stage, thereby reducing insulation resistance and the rate at which properly produced layered capacitors is obtained.
When the above-described sandblast method is used, water is not required because polishing is carried out by directly ejecting an abrasive onto the end surfaces 51a and 51b of the ceramic sintered bodies. However, it is necessary to carry out the troublesome step of holding the plurality of ceramic sintered bodies by a holder, thereby preventing a large number of ceramic sintered bodies to be produced efficiently.
Accordingly, it is an object of the present invention to provide a highly productive ceramic electronic part producing method which allows an internal electrode to be reliably exposed from an end surface of a ceramic sintered body by dry-barrel polishing that does not use water, so that delamination and deterioration in electrical properties do not easily occur, and so that the end surface of the ceramic sintered body can be efficiently polished.
To this end, according to the present invention, there is provided a method of producing a ceramic electronic part including an internal electrode in a ceramic sintered body and an external electrode electrically connected to the internal electrode at an outside surface of the ceramic sintered body, the method comprising the steps of:
obtaining the ceramic sintered body including the internal electrode; and
exposing the internal electrode from the outside surface of the ceramic sintered body by subjecting the ceramic sintered body to dry-barrel polishing.
When the dry-type barrel polishing is carried out, a dry-type centrifugal barrel device may be used, the dry-type centrifugal barrel device including a rotary plate that rotates around a rotary shaft as a center; a first drive source, connected to the rotary plate, for rotationally driving the rotary plate; a barrel pot connected to the rotary plate so as to rotate along with the rotary plate around the rotary shaft of the rotary plate and independently of the rotary plate, the barrel plate accommodating the ceramic sintered body therein; and a second drive source, connected to the barrel pot, for rotationally driving the barrel pot. In this case, the ceramic sintered body may be placed into the barrel pot, and the rotary plate and the barrel pot may be rotated.
When the dry-type barrel polishing is carried out, a barrel blast device may be used. Such a barrel blast device may include a barrel pot constructed so as to rotate around a central rotary shaft, the barrel pot having an opening; a blast nozzle for ejecting therefrom an abrasive towards the opening in the barrel pot; and a drive source, connected to the barrel pot, for rotationally driving the barrel pot. In this case, a plurality of the ceramic sintered bodies may be placed into the barrel pot, and as the barrel pot may be rotated while the abrasive is ejected from the blast nozzle to carry out the dry-barrel polishing.
At least a portion of the barrel pot may be formed of meshes or of a member with many holes.
The ceramic sintered body may be formed by obtaining an unsintered ceramic layered body and rounding a corner of the unsintered layered body by subjecting the unsintered ceramic layered body to the barrel polishing.
A dry centrifugal device may be used to carry out the barrel polishing. Such a device may include a first drive source, connected to a rotary plate, for rotationally driving the rotary plate; a barrel pot connected to the rotary plate so as to rotate along with the rotary plate around a rotary shaft of the rotary plate and independently of the rotary plate, the barrel plate accommodating the ceramic sintered body therein; and a second drive source, connected to the barrel pot, for rotationally driving the barrel pot.